Dynamic buffer for conveyor modules

Abstract

A method of operating an automotive production line including the steps of advancing a plurality of self-propelled carriages along a conveyor of the production line. The carriages are continuously advanced at a fixed operational speed and a fixed operational pitch to obtain a fixed processing time at a plurality of work stations along the production line. Any one of the carriages are stopped when a reduced pitch is obtained due to a stoppage of the immediately preceding carriage. The reduced pitch is less than the operational pitch and is preferably the minimum pitch available between the carriages. Stopped carriages are restarted when the reduced pitch returns to the operational pitch due to the restarting of the immediately preceding carriage. Production losses are reduced by continuing operations upstream of a stoppage to form a dynamic online buffer upstream of the stoppage. Production losses are further reduced when the dynamic online buffer is utilized to prevent the formation of a gap due to a subsequent stoppage located upstream of the dynamic online buffer. Production losses are even further reduced when previously existing gaps located upstream of the stoppage are closed as a result of continuing operations upstream of the stoppage.

What is claimed is: 
     
       1. A method of operating a production line comprising the steps of: advancing a plurality of self-propelled carriages in a forward direction along the production line at an operational speed and an operational pitch between adjacent ones of said carriages;   stopping a first one of said carriages from advancing in said forward direction;   stopping a second one of said carriages immediately following said first one of said carriages from advancing in said forward direction when a reduced pitch between said first and second ones of said carriages is obtained, wherein said reduced pitch is less than said operational pitch;   restarting said first one of said carriages to advance in said forward direction; and   restarting said second one of said carriages to advance in said forward direction after said step of restarting said first one of said carriages and advancement of said first one of said carriages has returned said reduced pitch to said operational pitch.   
     
     
       2. The method according to claim 1, wherein said reduced pitch corresponds to a minimum distance available between the carriages. 
     
     
       3. The method according to claim 1, further comprising the step of said second one of said carriages sensing the presence of said first one of said carriages to indicate stopping and restarting of the first one of said carriages. 
     
     
       4. The method according to claim 1, further comprising the step of said second one of said carriages sensing the distance to said first one of said carriages to indicate stopping and restarting of the first one of said carriages. 
     
     
       5. The method according to claim 1, further comprising the step of continuing to advance a third one of said carriages immediately preceding said first one of said carriages in said forward direction when said first one of said carriages is stopped to form a gap between said first and third ones of said carriages, said gap being greater than said operational pitch. 
     
     
       6. The method according to claim 5, wherein said gap is maintained when said first one of said carriages is restarted until there is a subsequent downstream stoppage of one of said carriages. 
     
     
       7. The method according to claim 1, wherein said self-propelled carriages are each advanced by a separate drive and control device carried thereon. 
     
     
       8. The method according to claim 1, wherein said self-propelled carriages are advanced unconnected to one another. 
     
     
       9. The method according to claim 1, wherein said operational speed is a fixed operation speed. 
     
     
       10. The method according to claim 1, wherein said operational pitch is a fixed operation pitch between adjacent ones of said carriages. 
     
     
       11. The method according to claim 1, wherein said step of stopping said second one of said carriages includes stopping said second one of said carriages without engaging said first one of said carriages. 
     
     
       12. A method of operating a production line comprising the steps of: advancing a plurality of self-propelled carriages along the production line in a forward direction at an operational speed and an operational pitch between adjacent ones of said carriages;   stopping a first one of said carriages from advancing in said forward direction when a reduced pitch between said first one of said carriages and a second one of said carriages immediately preceding said first one of said carriages is obtained due to a stoppage of one of said carriages, wherein said reduced pitch is less than said operational pitch; and   restarting the first one of said carriages to advance in said forward direction when forward advancement of said second one of said carriages has returned said reduced pitch to said operational pitch.   
     
     
       13. The method according to claim 12, wherein said reduced pitch corresponds to a minimum distance available between the carriages. 
     
     
       14. The method according to claim 12, further comprising the step of sensing the presence of a preceding carriage to indicate stopping and restarting of said preceding carriage. 
     
     
       15. The method according to claim 12, further comprising the step of sensing a distance to a preceding carriage to indicate stopping and restarting of said preceding carriage. 
     
     
       16. The method according to claim 12, further comprising the step of continuing advancement of a third one of said carriages immediately downstream of said stoppage in said forward direction to form a gap between said stoppage and said third one of said carriages, said gap being greater than said operational pitch. 
     
     
       17. The method according to claim 13, wherein said gap is maintained when said first one of said carriages is restarted until there is a subsequent downstream stoppage of one of said carriages. 
     
     
       18. The method according to claim 12, wherein said self-propelled carriages are each advanced by a separate drive and control device carried thereon. 
     
     
       19. The method according to claim 12, wherein said self-propelled carriages are advanced unconnected to one another. 
     
     
       20. The method according to claim 12, wherein said operational pitch is a fixed operation pitch between adjacent ones of said carriages. 
     
     
       21. The method according to claim 12, wherein said operational speed is a fixed operation speed. 
     
     
       22. The method according to claim 12, wherein said step of stopping said first one of said carriages includes stopping said first one of said carriages without engaging said second one of said carriages. 
     
     
       23. A method of operating a production line comprising the steps of: advancing a plurality of self-propelled carriages along the production line at an operational speed and with a fixed operational pitch between adjacent ones of said carriages, said self-propelled carriages being advanced unconnected to one another and each being advanced by separate drive and control devices carried thereon;   stopping a first one of said carriages;   stopping a second one of said carriages immediately following said first one of said carriages when a reduced pitch between said first and second ones of said carriages is obtained, said reduced pitch being less than said operational pitch;   continuing to advance a third one of said carriages immediately preceding said first carriage when said first one of said carriages is stopped to form a gap between said first and third ones of said carriages, said gap being greater than said operational pitch;   restarting said first one of said carriages, said gap being maintained when said first one of said carriages is restarted; and   restarting said second one of said carriages after advancement of said first one of said carriages has returned said reduced pitch to said fixed operational pitch.